The hydrocarbon mixtures, used as diesel fuel, have the undesired property of interacting with air and developing foam when filled into tanks such as storage tanks and fuel tanks of motor vehicles. This leads to a delay in the filling process as well as inadequate filling of the tanks. It is therefore customary to add defoamers to the diesel fuel. These defoamers should be effective at low concentrations and must not form any harmful residues when the diesel fuel undergoes combustion in the engine, nor should they affect the combustion of the fuel negatively. Correspondingly effective defoamers are described in numerous patent literature.
For example, the British patent 2,173,510 relates to a method for defoaming diesel fuel or jet fuel. For this method, an anti-foaming agent is added to the fuel. This anti-foaming agent consists essentially of an organopolysiloxane of the following formula EQU R.sub.3 SiO (R.sub.2 SiO).sub.x (RR'SiO).sub.y SiR.sub.3
wherein the ratio of x:y lies in the range of 1:1 to 9:1, PA1 each R group is a univalent hydrocarbon group and at least 80% of the R groups are methyl groups, PA1 each R' group is a substituted group of the general formula Q(OA).sub.n OZ, in which PA1 the copolymer has an average molecular weight so that the OA groups constitute 25 to 65% by weight of the calculated molecular weight of the copolymer, PA1 the copolymer being soluble in an organic solvent. The antifoaming agent is used at concentration of 1 to 100 and preferably 5 to 50 ppm, based on the diesel fuel. PA1 A is a group of the general formula ##STR2## wherein R.sup.1 represents a group of the formula --CR.sup.3 H--, in which PA1 R.sup.3 is a hydrogen or a univalent organic group, PA1 R.sup.2 is a group having the formula --CR.sup.4 H--CH.sub.3 or --(CH.sub.2).sub.3, in which PA1 R.sup.4 is a hydrogen or univalent organic group, PA1 v, w in each case are 0 or a whole number, the average value of v+w being 0 to 16, PA1 x, y are 0 or 1, x+y being 1 or 2, PA1 a=1, 2 or 3, PA1 b=0, 1 or 2, and PA1 c=1 or 2, the sum of b+c not exceeding 3. PA1 R.sup.2 are the same or different in the molecule, PA1 for defoaming diesel fuel in amounts of 0.5 to 50 ppm based on the diesel fuel. PA1 30 to 90% of all R.sup.2 groups can have the same meaning as the R.sup.1 groups, with the proviso that PA1 70 to 10% of the R.sup.2 groups consist of a mixture of R.sup.2A and R.sup.2B groups. PA1 R.sup.8 is a hydroxyl or alkoxy group, PA1 R.sup.9 is a hydrogen, alkyl or alkenyl group, PA1 p, q and r each is a number from 0 to 100, PA1 the sum of which is 1 to 200. PA1 10% by weight of the organofunctionally modified siloxane of Formula I, PA1 63% by weight of the polyether of Formula II, and PA1 27% by weight of emulsifier. PA1 10 to 40% by weight of the organofunctionally modified polysiloxane of Formula I, PA1 50 to 89% by weight of the polyether of Formula II, and PA1 1 to 10% by weight of emulsifier.
Q is a divalent group linked to a silicon atom, PA2 A is an alkylene group and at least 80% of these groups are ethylene groups, PA2 Z is a hydrogen group or an OCR" group, in which R" is a univalent group, PA2 n has a value of 5 to 25, and PA2 30 to 90% of R.sup.2 having the same meaning as R.sup.1, and PA2 70 to 10% of R.sup.2 consisting of a mixture of R.sup.2A and R.sup.2B groups, wherein the R.sup.2A groups are more polar than the R.sup.2B groups and the R.sup.2A groups are selected from the following groups: ##STR4## group, wherein R.sup.3 is a hydrogen or alkyl group, PA2 a is a number from 1 to 400, PA2 b is a number from 0 to 10,
The German Offenlegungsschrift 40 32 006 discloses a method for defoaming and/or degassing organic systems by adding an antifoaming agent containing an organopolysiloxane to these organic systems containing diesel oil and/or crude oil or cracking products thereof. As organopolysiloxane, a polymer is used, which consists of siloxane units of the general formula ##EQU1## wherein R is a univalent hydrocarbon group with 1 to 18 carbon atom (s) per group,
The siloxanyl-alkenediyl-bis-.omega.-hydroxy-polyoxyalkylenes and their synthesis are described in the DD patent 255 737.
The antifoaming agents for diesel fuels described above and others known from the state of the art have various disadvantages. For example, the silicon content of typical polysiloxane polyoxyalkylene copolymers is 10 to 15% by weight. For organopoly-siloxanes with alkenediyl-bis-.omega.-hydroxypolyoxyalkylenes, the silicon content is even 20 to 25% by weight. Since compounds with such a high silicon content can lead to undesirable silica depositions when combusted in the engine, there is a need for defoamers for diesel fuels with a lower silicon content or, at least, improved foam prevention and foam elimination, in order to be able to reduce the concentration at which these additives are used.
A further disadvantage of the known antifoaming agents consists in their frequent inadequate compatibility (miscibility) with the additive packages, which are added to the crude diesel oil for improving its properties. Additive packages are defined as mixtures of different additives, such as materials for improving the combustion behavior, materials for decreasing the formation of smoke, materials for decreasing the formation of harmful exhaust gases, inhibitors for decreasing corrosion in the engine and its parts, surface active substances, lubricants and the like. Such additive packages are described, for example, in the Japanese publication 05 132 682, the British patent 2,248,068 and in the journal Mineraloltechnik, 37(4), 20 pp. The additives of the additive package are dissolved in an organic solvent and form a stock concentrate, which is added to the crude diesel fuel. Anti-foaming agents with polar groups frequently cannot be incorporated uniformly into these additive packages or separate upon storage.